The present invention relates to coatings comprising a polymer and a mixture of carbon blacks as conductive fillers. The mixture of carbon blacks comprises more than one or at least two different varieties or types of carbon black, and preferably a graphite carbon black and a conductive carbon black other than graphite. Additional fillers can be used in addition to the mixture of carbon blacks. The coatings allow for tailoring of conductivity for use of the coatings in components useful in xerographic, including digital, processes. In preferred embodiments, the coatings are useful as coatings for fuser components such as, for example, fuser members including instant-on fuser members, pressure members, donor members, transfuse members and the like. In embodiments, the present coatings allow for the preparation and manufacture of coated components having excellent electrical, chemical and mechanical properties, including conductivity tailored to a desired conductivity range and controlled conductivity, wherein the conductivity of the fuser member is virtually unaffected by changes in temperature, relative humidity, and small changes in filler loadings. In addition, in embodiments, the present coatings are superior in coating reproducability and thickness control. Moreover, in embodiments, the warming-up period for the fuser member is decreased, and the power consumption of the fuser member is decreased, while allowing for high operating temperature and mechanical strength.
In a typical electrostatographic reproducing apparatus, a light image of an original to be copied is recorded in the form of an electrostatic latent image upon a photosensitive member and the latent image is subsequently rendered visible by the application of electroscopic thermoplastic resin particles which are commonly referred to as toner. The visible toner image is then in a loose powdered form and can be easily disturbed or destroyed. The toner image is usually fixed or fused upon a support which may be the photosensitive member itself or other support sheet such as plain paper.
Typically, the thermoplastic resin particles are fused to the substrate by heating to a temperature of between about 90.degree. C. to about 200.degree. C. or higher. It is important in the fusing process that no offset of the toner particles from the support to the fuser member take place during normal operations, because such toner particles offset onto the fuser member may subsequently transfer to other parts of the machine or onto the support in subsequent copying cycles, thus increasing the background or interfering with the material being copied there.
Several approaches to thermal fusing of electroscopic toner images have been described. These methods include providing the application of heat and pressure substantially concurrently by various means, a roll pair maintained in pressure contact, a belt member in pressure contact with a roll, a belt member in pressure contact with a heater, and the like. Heat may be applied by heating one or both of the rolls, plate members, or belt members.
Such heat fixing apparatii demonstrate problems due to the lengthy warm-up time required before the heating body is raised to a specified temperature. In some machines, the fuser member is in heated mode 90 to 100 percent of the time the machine is turned on. Because the fuser is heated at all times, there is an increased chance of overheating, and mechanical problems may result from the fuser member overheating or breaking down from overuse.
Moreover, with the fuser member continuously being heated, much energy is wasted. The Environmental Protection Agency has proposed new "energy star" guidelines for printers and copiers. Current fusers that operate in a continuous heat mode may not meet the expectations of a "green machine."
A preferred fusing system for copying and printing is the use of an "instant-on" fuser system, wherein the image on a copy substrate is fused by positioning the paper through a nip between a fuser roll and a pressure roll, the fuser roll and/or pressure roll comprising a high temperature plastic core substrate, a heat generating layer and a toner releasing layer (or heat transporting layer). The fuser converts electric energy directly to thermal energy, and is therefore more energy efficient. The instant-on fuser member is advantageous in that the warming-up period is reduced as the heater is quick to respond. In addition, the instant-on fuser member allows for a reduction in energy consumption because the heater is off when the machine is not copying.
Instant-on fusing systems as set forth above are well known and disclosed in, for example, U.S. Pat. No. 5,087,946 to Dalal et al., the disclosure of which is hereby incorporated by reference in its entirety. This reference discloses an instant-on fusing system including a fuser roll having a hollow plastic cylinder having a conductive fiber filler and having a relatively thin wall, a back up roll disposed in an engaging relationship, and a heating element disposed within the fuser roll.
Further preferred methods of fusing include transfuse methods, wherein the developed image is simultaneously transferred and fused to a copy substrate.
In order to increase thermal conductivity in fuser members, conductive fillers such as carbon have been added to fusing layers. For example, U.S. Pat. No. 5,084,738 discloses use of a resistive heating layer with resistivity ranging from 20 to 2000 ohm-cm in a fusing apparatus. The resistivity of the layer is achieved by adding conductive carbon fillers into a polymer layer. Also, U.S. Pat. No. 5,064,509 discloses a process for preparing a multi-layered belt which includes a thermoplastic film forming polymer which may be comprised of polyurethane or prepolymers of polyimide, and which may include conductive particles such as carbon black, graphite or titanium dispersed therein.
There exists a need for a fuser member surface which has a stable conductivity in the desired conductivity range which is virtually unaffected by changes in temperature, relative humidity, other environmental changes, and is virtually unaffected by small changes in filler loadings. There further exists a specific need for a fusing system member which is quick to heat up, which allows for decreased use of energy, and in which the conformability and low surface energy properties of the release layer are not affected. There further exists a need for a fusing system which provides for good release properties and a decrease in the occurrence of hot offset. Moreover, there exists a need for improved coating reproducability and thickness control for carbon filled polymer coatings.